Generally, a terminal uses a threshold in deciding reception success information (ACK) or reception failure information (NCK) via forward-acknowledgement channel (hereinafter abbreviated F-ACKCH).
FIG. 1 is a diagram for explaining a general method of deciding a reception acknowledgment (ACK) according to a threshold.
Referring to FIG. 1, it is decided as acknowledgement (ACK) if a reception level is equal to or greater than a threshold. And, it is decided as non-acknowledgement (NCK) if a reception level is smaller than a threshold. A false alarm probability for deciding a NCK signal as an ACK signal incorrectly and a missing probability for deciding an ACK signal as a NCK signal are preferentially determined. And, a threshold is adjusted to fit the probabilities. The false alarm probability for deciding a NCK signal as an ACK signal incorrectly is usually set lower in general.
However, if the false alarm probability is incorrect, failure is regarded as success. Hence, retransmission by signaling is needed after a predetermined time has passed.